Far from a simple waypoint system that sends you back the way you came, both patents note that the system "can determine when a vehicle in which the mobile device is located has entered a parked state," automatically.

This can be achieved either by utilizing an iPhone's built-in accelerometer to determine the difference between in-motion driving and a stopped, parked state, or via a data connection with the vehicle itself, which would then tell the device that the car is indeed parked. Once this is determined, the user's path away from the vehicle is tracked to allow for the return trip to be plotted.

As someone who hates going to the grocery store for multiple reasons -- one of which being that I never remember to mentally note my parking space -- this could certainly come in handy. As with all patents, however, we may very well never see this system make it into a device, though it certainly seems to be technically doable with existing technology.